Flattening permission trees in a virtualization environment

ABSTRACT

A virtualization manager receives a permission request indicating a user and an entity in a virtual machine system. The virtualization manager flattens a permissions database to generate a flattened database view. Using the flattened database view, the virtualization manager determines whether the user has permission to access the entity in the virtual machine system and returns an indication of whether the user has permission to access the entity in the virtual machine system.

TECHNICAL FIELD

This disclosure relates to the field of virtualization and, inparticular, to flattening permission trees in a virtualizationenvironment.

BACKGROUND

Virtualization allows multiplexing of the underlying host machinebetween different virtual machines. The host computer allocates acertain amount of its resources to each of the virtual machines. Eachvirtual machine is then able to use the allocated resources to executeapplications, including operating systems (referred to as guestoperating systems). The software layer providing the virtualization iscommonly referred to as a hypervisor and is also known as a virtualmachine monitor (VMM), a kernel-based hypervisor or a host operatingsystem. The hypervisor emulates the underlying hardware of the hostcomputer, making the use of the virtual machine transparent to the guestoperating system and the user of the virtual machine.

Virtual machines can be provided by a centralized host that is coupledto multiple clients over a network. Each client can provide a virtualdesktop environment indistinguishable from a physical desktop. A largeorganization with many different departments and multiple offices atvarious locations may have a system with thousands of virtual machines.Management of numerous virtual machines is a complex task that requiresa large degree of system scalability.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings.

FIG. 1 is a block diagram illustrating an exemplary network architecturein which embodiments of the present invention may operate.

FIG. 2 is a block diagram illustrating a permission control system,according to an embodiment.

FIG. 3 is a flow diagram illustrating a method for facilitating controlof permissions in a virtualization environment, according to anembodiment.

FIG. 4 is a flow diagram illustrating a method for processing permissionrequests using a flattened permission tree, according to an embodiment.

FIG. 5 is a flow diagram illustrating a method for flattening permissiontrees, according to an embodiment.

FIG. 6 is a block diagram illustrating a computer system, according toan embodiment.

DETAILED DESCRIPTION

The following description sets forth numerous specific details such asexamples of specific systems, components, methods, and so forth, inorder to provide a good understanding of several embodiments of thepresent invention. It will be apparent to one skilled in the art,however, that at least some embodiments of the present invention may bepracticed without these specific details. In other instances, well-knowncomponents or methods are not described in detail or are presented insimple block diagram format in order to avoid unnecessarily obscuringthe present invention. Thus, the specific details set forth are merelyexemplary. Particular implementations may vary from these exemplarydetails and still be contemplated to be within the scope of the presentinvention.

Described herein is a method and system for flattening permission treesin a virtualization environment. In one embodiment, servers hostingvirtual machines are coupled to a host controller that associatesvirtual machines with labels representing distinct virtual machineparameters such as a geographic location of a virtual machine, adepartment of a virtual machine user, a technical characteristic of avirtual machine, etc. These labels may be organized into a tree havinghierarchical relationships. For example, location label “France” may bea parent of department labels “Human Resources,” “Finance” and“Billing.” In some cases, these child labels may inherit the permissionsof the parent label.

The host controller may also maintain multiple roles, where each roledefines a set of allowed actions such as viewing virtual machines,adding virtual machines, editing virtual machines, etc. The hostcontroller associates users with appropriate roles and labels to form ahierarchical permission tree. The host controller then uses theseassociations to facilitate control over user actions pertaining toentities in a virtual machine system. For example, a specific userwithin a company may be associated with the role of a virtual machinemanager to allow this user to add, delete and modify virtual machines orother entities. In addition, this user may be associated with labels“Finance” and “Billing” to permit the user to perform the above actionsonly with respect to virtual machines from the Finance and Billingdepartments.

In certain embodiments, permissions for access to virtual machines maybe defined based on either the labels, the roles, or a combination ofthe two. Defining permissions in this manner is generally moreconvenient than defining permissions for every individual in anorganization. That way, if the need arises to changes a user'spermissions or add a new virtual machine, the user may simply beassigned to a role and the virtual machine may be given a label. Theuser or virtual machine will then automatically be assigned thepredefined permissions associated with the role or label.

Despite the convenience provided by this system in assigningpermissions, it can make verifying permissions significantly morecomplicated. For example, if a user requests access to a virtual machineor an administrator or program requests the permissions for a certainuser or virtual machine, there is no single place to view the specificpermissions for a particular user or machine. Generally multipleoperations will be needed to verify the permissions, for exampleincluding the queries: Does the user have permission for the requestedvirtual machine?; Does the role(s) to which the user is assigned havepermission for the requested virtual machine?; Does the user havepermission for a parent label of the virtual machine?; Does the role(s)to which the user is assigned have permission for a parent label of thevirtual machine?; etc.

In order to simplify the permission verification process, the hostcontroller can flatten a permissions database containing these variouspermissions to create a single view that includes the permissions foreach combination of user and entity in the virtual machine system. Thisdatabase view may include a stored query accessible as a virtual tablein the database or other data structure. The view may not form part ofthe physical schema of the database, but rather may include a dynamic,virtual table computed from the data in the database. This database viewmay be self-descriptive, such that applications accessing the databaseneed not include additional code to process permission verifications.Users and applications accessing the database view may appreciateincreased performance attributable to the simplicity of the verificationprocess, and the need for fewer database queries. The self-descriptiveview will also be available to applications across varying programminglanguages, without the need for proprietary permission verificationlogic.

In other embodiments, the same flattening techniques may be used forother databases. For example, a database containing data other thanpermissions for access to virtual machines may be flattened and accessedin the same or similar manner as described below, allowing the requestorto obtain the information with only a single query. In otherembodiments, the same flattening techniques may also be used for anysystem that has some form of a permissions system.

FIG. 1 illustrates an exemplary network architecture 100 in whichembodiments of the present invention may operate. The networkarchitecture 100 includes one or more host servers 103 coupled toclients 101 over a network 102. The network 102 may be a private network(e.g., a local area network (LAN), wide area network (WAN), intranet,etc.) or a public network (e.g., the Internet). The host servers 103 mayalso be coupled to a host controller 107 (via a network or directly).Host controller 107 may be an independent machine such as a servercomputer, a desktop computer, etc. Alternatively, the host controller107 may be part of the host server 103.

In one embodiment, the clients 101 may include computing devices thathave a wide range of processing capabilities. Some or all of the clients101 may be thin clients, which serve as access terminals for users anddepend primarily on the host servers 103 for processing activities. Forexample, the client 101 may be a desktop computer, laptop computer,cellular phone, personal digital assistant (PDA), etc. The client 101may run client applications such as a Web browser. The client 101 mayalso run other client applications, which receive multimedia datastreams or other data from the host server 103 and re-direct thereceived data to a local display or other user interface.

Host servers 103 may include server computers or any other computingdevices capable of running one or more virtual machines 131. Eachvirtual machine 131 runs a guest operating system (OS) that may bedifferent from one virtual machine to another. The guest OS may includeMicrosoft Windows, Linux, Solaris, Mac OS, etc. The host server 103 mayinclude a hypervisor 132 that emulates the underlying hardware platformfor the virtual machines 131. The hypervisor 132 may also be known as avirtual machine monitor (VMM), a kernel-based hypervisor or a hostoperating system.

Each virtual machine 131 can be accessed by one or more of the clients101 over the network 102 and can provide a virtual desktop for theclient(s) 101. From the user's point of view, the virtual desktopfunctions as a physical desktop (e.g., a personal computer) and isindistinguishable from a physical desktop. Each virtual machine 131 maybe linked to one or more virtual disks 133. These virtual disks 133 canbe logical partitions of a physical disk managed by hypervisor 132, canbe cloud based storage devices, or can be some other type of virtualstorage device. In one embodiment, virtual disks 133 may form a whole orpart of a logical data center. In one embodiment, virtual machines 131and virtual disks 133, together with host servers 103, may becollectively referred to as entities in a virtual machine system.

The virtual machines 131 and virtual disks 133 are managed by the hostcontroller 107. The host controller 107 ensures that operationspertaining to individual virtual machines 131 are performed byappropriate users. For example, in an organization having offices indifferent geographic locations and a large number of virtual machines ineach location, an information technology (IT) director may be allowed tomake any changes with respect to virtual machines 131 while a systemadministrator responsible for a specific office may only be allowed toadminister virtual machines in this specific office. In addition, anoffice may have several departments, with each department having adesignated IT technician allowed to oversee operation of virtualmachines associated with the respective department.

In one embodiment, the host controller 107 includes a virtualizationmanager 109 that sets permissions for actions pertaining to variousentities in the virtual machine system using hierarchical labeling. Inone embodiment, the entities in the virtual machine system may includevirtual machines, virtual disks, hosts or host servers, logical datacenters, or other entities. For ease of explanation, additionalreference to these entities may refer to virtual machines, however, itshould be understood that the explanation may apply equally to otherentities of the virtual machine system in other embodiments. Inparticular, the virtualization manager 109 associates each virtualmachine 131 with one or more labels representing distinct virtualmachine parameters. For example, a virtual machine 131 may be associatedwith labels representing the geographic location of the virtual machine131 such as a region label (e.g., Europe), a country label (e.g.,France) and a city label (e.g., Paris). In addition, the virtual machine131 may be associated with labels representing a positioning of a userof the virtual machine 131 within the organization (e.g., a departmentlabel, a group label, or a title label). The virtual machine 131 mayalso be associated with labels representing technical characteristics ofa virtual machine (e.g., a memory allocation label, an operating systemlabel, etc.), or with any other labels. The virtualization manager 109stores associations between virtual machines 131 and respective labelsin a database 106 residing on a data storage device 105. In addition,the virtualization manager 109 assigns roles to various users and/orvarious groups of users, where each role defines a set of actionspermitted to be performed by a user or a group of users with respect tovirtual machine 131. Further, the virtualization manager 109 associatesthe users and/or groups of users with respective labels to allow eachuser to perform actions only with respect to the virtual machines 131having the matching labels. The virtualization manager 109 storesassociations of users and/or groups of users with respective roles andlabels in the database 106 residing on the data storage device 105. Thedata storage device 105 may share the machine with the host controller107 (e.g., a disk drive in the host controller computer) or be anindependent device coupled to the host controller directly or via anetwork (e.g., as a network-attached storage device (NAS)).

FIG. 2 is a block diagram illustrating a permission control system (PCS)200 in accordance with one embodiment of the present invention. The PCS200 includes a virtualization manager 202, which may be similar tovirtualization manager 109, and a management database 204, which may behosted by data storage device 105.

The virtualization manager 202 may include a user interface module 206,a label manager 208 and a permission manager 216. The user interfacemodule 206 may provide a labels user interface for specifying labels andhierarchical relationships between the labels. Each label may be anobject having an identifier. For example, each label may be an object inthe form of a file (e.g., a text file, a XML file, etc.).

The labeling hierarchy can be in the form of a tree where nodesrepresent labels and edges represent relationships between the labels.In particular, the top node in the tree can represent an organizationlabel (e.g., a company, a university, a library, etc.). The organizationlabel can have child labels such as a division label representing adivision within the organization (e.g., Sony Ericsson, Sony PicturesEntertainment, etc.), a location label representing a geographiclocation (e.g., Europe, North America, Middle East, etc.), a technicalcomponent label representing a machine component type (e.g., hardware,operating system, application, etc.), etc. These labels may, in turn, beparents of other labels. For example, the division label can be a parentof department labels representing departments of virtual machine userswithin the division, with each department label being a parent of grouplabels representing groups of virtual machine users within thedepartment. The location label can be a parent of country labelsrepresenting different countries, with each country being a parent ofcity labels. The technical component label can be a parent of technicalcharacteristic labels representing specific technical characteristics ofa virtual machine (e.g., a memory allocation parameter, a graphicsparameter, etc.).

The labeling hierarchy provides an easy and convenient way of taggingvirtual machines with a wide variety of labels and definingrelationships between these labels. Associations between the labels andrespective virtual machines are stored in the management database 204(e.g., label table 210) using identifiers of virtual machines andidentifiers of labels. Thus, label table 210 may define permissions forthe virtual machines based on the label assigned to each virtualmachine. In one embodiment, child labels may inherit the permissions ofparent labels, according to the label hierarchy. In one embodimentlabels in the hierarchy may be assigned to other objects besides virtualmachines. For example, host server 103 may have a label that is a parentof the label assigned to virtual machine 131 in the hierarchy. In thiscase, a user with permissions for host server 103 may also have the samepermissions for the virtual machine 131 running on that host server 103.

The user interface module 206 may also provide a roles user interfacethat receives user input identifying various user roles (e.g., ITdirector, system administrator, virtual machine manager, end user, etc.)and actions permitted for each user role. Information identifying theuser roles and corresponding permitted actions is stored in themanagement database 204 (e.g., in a role table 214). Thus, role table214 may define permissions for the actions users assigned to a role areallowed to perform on certain virtual machines or other objects.

The user interface module 206 may further provide a permissions userinterface that receives user input assigning roles to specific usersand/or groups of users and user input associating users and/or groups ofusers with labels. Associations of users and/or groups of users withcorresponding roles and labels are stored in the management database 204(e.g., in a user permission table 212). In one embodiment, if a user ispart of one or more groups, the user has the same roles and labels asthose associated with the user's group(s). In addition to grouppermissions, the user may have individual permissions based on roles andlabels assigned to this specific user. These permissions may be storedin user permission table 212.

The label manager 208 handles user requests pertaining to labels. Forexample, a system administrator may need to know parameters of aspecific virtual machine, or virtual machines that have one or moreparameters in common. Upon receiving a system administrator request, thelabel manager 208 searches the management database 204 (e.g., the labeltable 210) and retrieves the requested information. In anotherembodiment, the permissions in label table 210, user permission table212 and role table 214 may be stored together in a single table, butstill be defined separately.

The permission manager 216 controls user actions pertaining to virtualmachines. In particular, the permission manager 216 receives a userrequest to perform a certain action concerning a virtual machine (e.g.,modify a virtual machine or delete a virtual machine) and issues a queryto management database 204 to create a flattened view 218, or consults aflattened view 218 if one was previously created. Permission manager 216may consult the flattened view 218 to determine if the user has thenecessary permissions for the requested virtual machine. Flattenedpermission view 218 may combine permissions defined for particularlabels (e.g., from label table 210), users (e.g., from user permissiontable 212), and/or roles (e.g., from role table 214) to includeindividual permissions for each combination of user and virtual machine.This flattened view 218 may include a stored query accessible as avirtual table in the database 204 or other data structure. The view 218may not form part of the physical schema of the database 204, but rathermay include a dynamic, virtual table computed from the data in thedatabase 204. This flattened view 218 may be self-descriptive, such thatapplications accessing the database 204 need not include additional codeto process permission verifications. As discussed above, permissionmanager 216 need only make a single query and the flattened view 218returns a binary result of yes/no, true/false, etc. If the permissiondetermination is negative, the permission manager 216 denies the userrequest. Otherwise, if the determination is positive, the permissionmanager 216 allows the requested action to proceed.

FIG. 3 is a flow diagram illustrating one embodiment of a method 300 forfacilitating control of permissions in a virtualization environment. Themethod 300 may be performed by processing logic that may comprisehardware (e.g., circuitry, dedicated logic, programmable logic,microcode, etc.), software (e.g., instructions run on a processingdevice to perform hardware simulation), or a combination thereof. In oneembodiment, the method 300 is performed by a host controller (e.g., hostcontroller 107 of FIG. 1).

Referring to FIG. 3, at block 310, method 300 begins with associatingvirtual machines with labels. In one embodiment, the associations areperformed based on user input. Alternatively, processing logic mayassociate a label with a virtual machine automatically upon detecting acertain event (e.g., when a user of a virtual machine moves to a newdepartment within a company). At block 320, method 300 stores the labelsin association with respective virtual machines in a database 106.

At block 330, method 300 associates users and/or groups of users withroles and virtual machine labels. In one embodiment, the associationsare performed based on user input. Alternatively, processing logic mayassociate a user with a role and/or a label automatically upon detectinga certain event (e.g., when a user's title changes, when a user moves toan office in a different location, etc.). At block 340, method 300stores user identifiers and/or user group identifiers in associationwith respective roles and labels in a database.

At block 350, method 300 controls user actions pertaining to virtualmachines based on corresponding user roles and labels. In particular,for each user request to perform a certain action concerning a virtualmachine (e.g., modify a virtual machine or delete a virtual machine),processing logic determines the roles of the user and the labelsassigned to the user, and decides whether to allow the requested actionbased on the corresponding roles and labels. In some embodiments, thisdetermination is performed using roles and labels associated with theuser. In other embodiments, this determination is performed using rolesand labels associated with the user's group(s). In yet otherembodiments, the determination is performed by combining roles andlabels associated with the user's group(s) with roles and labelsassociated with the user individually.

FIG. 4 is a flow diagram illustrating method for processing permissionrequests using a flattened permission tree, according to an embodimentof the present invention. The method 400 may be performed by processinglogic that comprises hardware (e.g., circuitry, dedicated logic,programmable logic, microcode, etc.), software (e.g., instructions runon a processing device to perform hardware simulation), or a combinationthereof. In one embodiment, method 400 may be performed byvirtualization manager 202, as shown in FIG. 2.

Referring to FIG. 4, at block 410, method 400 receives a permissionrequest. The permission request may specify one or more of an individualuser, a requested action and a virtual machine. For example, thepermission request may include a request from a user to perform anaction on a particular virtual machine, a request for a list of virtualmachines that an individual user can perform a certain action on, orsome other request. In one embodiment, virtualization manager 109running on host controller 107 receives the request from one of clientmachines 101. In another embodiment, the request may be received from asystem administrator, from a user, from an application or programrunning on one of host server 103 or client machine 101, or from someother source.

At block 420, method 400 determines whether the permissions database 204has been flattened. In one embodiment, permission manager 216 maydetermine if a flattened permission view 218 exists in managementdatabase 204. If at block 420, method 400 determines that thepermissions database 204 has not been flattened, at block 430, method400 generates a flattened database view 218. In one embodiment,permission manager 216 executes a query, the results of which are storedas flattened permission view 218. Additional details of creatingflattened permission view 218 are described below with respect to FIG.5. If at block 420, method 400 determines that the permissions database204 has been flattened, method 400 proceeds to block 440.

At block 440, method 400 determines, using the flattened permission view218, if the user is permitted to perform the requested action on thespecified virtual machine. Since flattened permission view 218 definespermissions for each combination of a user and virtual machine,permission manager 216 may need only make a single query to flattenedpermission view 218 to determine whether the requested action ispermitted. For example, permission manager 216 may query flattenedpermission view 218 for an entry containing the specified user andvirtual machine. If an entry exists designating the requested action, atblock 450, method 400 may permit the requested action. If no entryexists for that combination, at block 460, method 400 may deny therequested action. In another embodiment, an entry may exist specificallydenying permission for the requested action, in which case, method 400would also deny the requested action at block 460.

At block 470, method 400 may optionally return an indication of thepermission determination made at blocks 440-460. For example, permissionmanager 216 may send a message to the requestor who sent the requestreceived at block 410, indicating the results of the determination(i.e., permission granted/denied, a list of virtual machines on whichthe user may perform one or more actions, etc.). In another embodiment,rather than returning the indication, method 400 may simply perform ordeny the requested action on the specified virtual machine.

FIG. 5 is a flow diagram illustrating method for flattening permissiontrees, according to an embodiment of the present invention. The method500 may be performed by processing logic that comprises hardware (e.g.,circuitry, dedicated logic, programmable logic, microcode, etc.),software (e.g., instructions run on a processing device to performhardware simulation), or a combination thereof. In one embodiment,method 400 may be performed by virtualization manager 202, as shown inFIG. 2.

Referring to FIG. 5, at block 510, method 500 identifies a user. Theuser may be, for example a user specified in a request. However, sincethe process 500 may be repeated for each user, some other user may beidentified at block 510. For example, the user may be identifiedalphabetically, by seniority, randomly, or in some other manner.

At block 520, method 500 identifies one or more virtual machines forwhich the identified user has explicit permissions defined. For example,permission manager 216 may consult user permission table 212 to locateentries in user permission table 212 corresponding to the identifieduser. Each entry may include explicit permissions for the user relatingto one or more virtual machines. At block 530, method 500 identifieschild labels of the virtual machines for which the user has explicitpermissions. As described above, each virtual machine may be assigned alabel from a hierarchical label systems. For example, label manager 208of virtualization manager 202 may consult label table 210 to determinethe labels of the virtual machines identified at block 520 and, usingthe hierarchy, any child labels of the determined labels. In oneembodiment, virtual machines assigned these child labels may inherit thepermissions of the child labels. Thus, when a user has permissions for avirtual machine having a first label, the user may also have permissionsfor virtual machines having the child label of the first label.

At block 540, method 500 identifies roles to which the user is assigned.As described above, a user may be assigned to one or more roles withinan organization, for purposes of assigning similar permissions to agroup of people. At block 550, method 500 identifies one or more virtualmachines for which the role to which the user is assigned haspermissions. For example, permission manager 216 may consult role table214 to locate entries in role table 214 corresponding to the identifiedrole. Each entry may include explicit permissions for the role relatingto one or more virtual machines.

At block 560, method 500 identifies child labels of the virtual machinesfor which the role has explicit permissions. For example, label manager208 of virtualization manager 202 may consult label table 210 todetermine the labels of the virtual machines identified at block 550and, using the hierarchy, any child labels of the determined labels. Inone embodiment, virtual machines assigned these child labels may inheritthe permissions of the child labels. Thus, when a role has permissionsfor a virtual machine having a first label, the role may also havepermissions for virtual machines having the child label of the firstlabel.

At block 570, method 500 creates an entry in flattened permission view218 for each unique combination of a user and a virtual machine. Forexample, permission manager 216 may create a separate entry for the useridentified at block 510 and each of the virtual machines identified atblocks 520-560 indicating that the user has permissions on each of theidentified virtual machines. Since each combination has a separateentry, a requestor may need only make a single query of flattenedpermission view 218 to determine whether a user has permissions for acertain virtual machine.

FIG. 6 illustrates a diagrammatic representation of a machine in theexemplary form of a computer system 600 within which a set ofinstructions, for causing the machine to perform any one or more of themethodologies discussed herein, may be executed. In alternativeembodiments, the machine may be connected (e.g., networked) to othermachines in a local area network (LAN), an intranet, an extranet, or theInternet. The machine may operate in the capacity of a server or aclient machine in a client-server network environment, or as a peermachine in a peer-to-peer (or distributed) network environment. Themachine may be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, switch or bridge, or any machinecapable of executing a set of instructions (sequential or otherwise)that specify actions to be taken by that machine. Further, while only asingle machine is illustrated, the term “machine” shall also be taken toinclude any collection of machines that individually or jointly executea set (or multiple sets) of instructions to perform any one or more ofthe methodologies discussed herein. In one embodiment, computer system600 may be representative of a computing device, such as client 101,host server 103 or host controller 107 running virtualization manager109.

The exemplary computer system 600 includes a processing device 602, amain memory 604 (e.g., read-only memory (ROM), flash memory, dynamicrandom access memory (DRAM) (such as synchronous DRAM (SDRAM) or RambusDRAM (RDRAM), etc.), a static memory 606 (e.g., flash memory, staticrandom access memory (SRAM), etc.), and a data storage device 618, whichcommunicate with each other via a bus 630. Any of the signals providedover various buses described herein may be time multiplexed with othersignals and provided over one or more common buses. Additionally, theinterconnection between circuit components or blocks may be shown asbuses or as single signal lines. Each of the buses may alternatively beone or more single signal lines and each of the single signal lines mayalternatively be buses.

Processing device 602 represents one or more general-purpose processingdevices such as a microprocessor, central processing unit, or the like.More particularly, the processing device may be complex instruction setcomputing (CISC) microprocessor, reduced instruction set computer (RISC)microprocessor, very long instruction word (VLIW) microprocessor, orprocessor implementing other instruction sets, or processorsimplementing a combination of instruction sets. Processing device 602may also be one or more special-purpose processing devices such as anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), a digital signal processor (DSP), network processor,or the like. The processing device 602 is configured to executeprocessing logic 626 for performing the operations and steps discussedherein.

The computer system 600 may further include a network interface device608. The computer system 600 also may include a video display unit 610(e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), analphanumeric input device 612 (e.g., a keyboard), a cursor controldevice 614 (e.g., a mouse), and a signal generation device 616 (e.g., aspeaker).

The data storage device 618 may include a machine-accessible storagemedium 628, on which is stored one or more set of instructions 622(e.g., software) embodying any one or more of the methodologies offunctions described herein. The instructions 622 may also reside,completely or at least partially, within the main memory 604 and/orwithin the processing device 602 during execution thereof by thecomputer system 600; the main memory 604 and the processing device 602also constituting machine-accessible storage media. The instructions 622may further be transmitted or received over a network 620 via thenetwork interface device 608.

The machine-readable storage medium 628 may also be used to storeinstructions for flattening permission trees, as described herein. Whilethe machine-readable storage medium 628 is shown in an exemplaryembodiment to be a single medium, the term “machine-readable storagemedium” should be taken to include a single medium or multiple media(e.g., a centralized or distributed database, and/or associated cachesand servers) that store the one or more sets of instructions. Amachine-readable medium includes any mechanism for storing informationin a form (e.g., software, processing application) readable by a machine(e.g., a computer). The machine-readable medium may include, but is notlimited to, magnetic storage medium (e.g., floppy diskette); opticalstorage medium (e.g., CD-ROM); magneto-optical storage medium; read-onlymemory (ROM); random-access memory (RAM); erasable programmable memory(e.g., EPROM and EEPROM); flash memory; or another type of mediumsuitable for storing electronic instructions.

Although the operations of the methods herein are shown and described ina particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

What is claimed is:
 1. A method comprising: receiving a permissionrequest, the request indicating a user and an entity in a virtualmachine system; flattening, by a processing device, a permissionsdatabase associated with the virtual machine system to generate aflattened database view, wherein the permissions database to storedescriptive labels of entities in the virtual machine system, andwherein the flattened database view defines permissions for the user toaccess the entities in the virtual machine system in view of thedescriptive labels, wherein flattening the permissions databasecomprises: identifying a first set of entities in the virtual machinesystem for which the user has explicit permissions defined in thepermissions database, identifying a second set of entities in thevirtual machine system for which a role to which the user is assignedhas explicit permissions defined in the permissions database;identifying a third set of entities in the virtual machine system thatinherit the explicit permissions of entities in the first and secondsets of entities, wherein entities in the third set of entities areassigned child labels in a labeling hierarchy of entities in the virtualmachine system, and creating a separate entry in the flattened databaseview for each unique combination of the user and one of the entities inthe first, second and third sets of entities in the virtual machinesystem, wherein the flattened database view comprises a stored queryaccessible as a virtual table in the permissions database computed fromdata stored in the permissions database; determining, using theflattened database view, whether the user has permission to access theentity in the virtual machine system, wherein determining whether theuser has permission to access the entity in the virtual machine systemcomprises issuing a single query to the flattened database view for anentry comprising the user and the entity; and returning an indication ofwhether the user has permission to access the entity in the virtualmachine system.
 2. The method of claim 1, wherein the permission requestis received from a client device.
 3. The method of claim 1, whereinflattening the permissions database comprises: identifying a firstentity in the virtual machine system for which the user has explicitpermissions defined in the permissions database; and identifying asecond entity in the virtual machine system that is a child of the firstentity using the labeling hierarchy of entities in the virtual machinesystem.
 4. The method of claim 3, wherein flattening the permissionsdatabase further comprises: identifying the role to which the user isassigned; identifying a third entity in the virtual machine system forwhich the role has permissions defined in the permissions database; andidentifying a fourth entity in the virtual machine system that is achild of the third entity using the labeling hierarchy of entities inthe virtual machine system.
 5. The method of claim 4, wherein flatteningthe permissions database further comprises: creating a separate entry inthe flattened database view for each unique combination of the user andone of the first, second, third and fourth entities.
 6. The method ofclaim 1, wherein the indication of whether the user has permission toaccess the entity is affirmative if the entry in the flattened databaseview comprising the user and the entity is located.
 7. The method ofclaim 1, wherein the indication of whether the user has permission toaccess the entity is negative if the entry in the flattened databaseview comprising the user and the entity is not located.
 8. The method ofclaim 1, wherein the entity in the virtual machine system comprises atleast one of a virtual machine, a virtual disk, a host server, or avirtual data center.
 9. A system comprising: a processing device; amemory coupled to the processing device; and a virtualization manager,executable by the processing device from the memory, to: receive apermission request from a client, the request indicating a user and anentity in a virtual machine system; flatten a permissions databaseassociated with the virtual machine system to generate a flatteneddatabase view, wherein the permissions database to store descriptivelabels of entities in the virtual machine system, wherein the flatteneddatabase view defines permissions for the user to access the entities inthe virtual machine system in view of the descriptive labels, wherein togenerate the flattened database view, the virtualization manager isexecutable to: identify a first set of entities in the virtual machinesystem for which the user has explicit permissions defined in thepermissions database, identify a second set of entities in the virtualmachine system for which a role to which the user is assigned hasexplicit permissions defined in the permissions database, identify athird set of entities in the virtual machine system that inherit theexplicit permissions of entities in the first and second sets ofentities, wherein entities in the third set of entities are assignedchild labels in a labeling hierarchy of entities in the virtual machinesystem, and create a separate entry in the flattened database view foreach unique combination of the user and one of the entities in thefirst, second and third sets of entities in the virtual machine system,wherein the flattened database view comprises a stored query accessibleas a virtual table in the permissions database computed from data storedin the permissions database; determine whether the user has permissionto access the entity in the virtual machine system using the flatteneddatabase view, wherein to determine whether the user has permission toaccess the entity in the virtual machine system, the virtualizationmanager is executable to issue a single query to the flattened databaseview for an entry comprising the user and the entity; and return anindication of whether the user has permission to access the entity inthe virtual machine system.
 10. The system of claim 9, wherein toflatten the permissions database, the virtualization manager isexecutable to: identify a first entity in the virtual machine system forwhich the user has explicit permissions defined in the permissionsdatabase; and identify a second entity in the virtual machine systemthat is a child of the first entity using the labeling hierarchy ofentities in the virtual machine system.
 11. The system of claim 10,wherein to flatten the permissions database, the virtualization manageris further executable to: identify the role to which the user isassigned; identify a third entity in the virtual machine system forwhich the role has permissions defined in the permissions database; andidentify a fourth entity in the virtual machine system that is a childof the third entity using the labeling hierarchy of entities in thevirtual machine system.
 12. The system of claim 11, wherein to flattenthe permissions database, the virtualization manager is furtherexecutable to: create a separate entry in the flattened database viewfor each unique combination of the user and one of the first, second,third and fourth entities.
 13. The system of claim 9, wherein theindication of whether the user has permission to access the entity isaffirmative if the entry in the flattened database view comprising theuser and the entity is located.
 14. The system of claim 9, wherein theindication of whether the user has permission to access the entity isnegative if the entry in the flattened database view comprising the userand the entity is not located.
 15. The system of claim 5, wherein theentity in the virtual machine system comprises at least one of a virtualmachine, a virtual disk, a host server, or a virtual data center.
 16. Anon-transitory machine-readable storage medium storing instructionswhich, when executed, cause a processing device to: receive a permissionrequest, the request indicating a user and an entity in a virtualmachine system; flatten a permissions database associated with thevirtual machine system to generate a flattened database view, whereinthe permissions database to store descriptive labels of entities in thevirtual machine system, and wherein the flattened database view definespermissions for the user to access the entities in the virtual machinesystem in view of the descriptive labels, wherein to flatten thepermissions database, the instructions to cause the processing deviceto: identify a first set of entities in the virtual machine system forwhich the user has explicit permissions defined in the permissionsdatabase, identify a second set of entities in the virtual machinesystem for which a role to which the user is assigned has explicitpermissions defined in the permissions database, identify a third set ofentities in the virtual machine system that inherit the explicitpermissions of entities in the first and second sets of entities,wherein entities in the third set of entities are assigned child labelsin a labeling hierarchy of entities in the virtual machine system, andcreate a separate entry in the flattened database view for each uniquecombination of the user and one of the entities in the first, second andthird sets of entities in the virtual machine system, wherein theflattened database view comprises a stored query accessible as a virtualtable in the permissions database computed from data stored in thepermissions database; determine, using the flattened database view,whether the user has permission to access the entity in the virtualmachine system, wherein to determine whether the user has permission toaccess the entity in the virtual machine system, the instructions tocause the processing device to issue a single query to the flatteneddatabase view for an entry comprising the user and the entity; andreturn an indication of whether the user has permission to access theentity in the virtual machine system.
 17. The non-transitorymachine-readable storage medium of claim 16, wherein to flatten thepermissions database, the instructions to cause the processing deviceto: identify a first entity in the virtual machine system for which theuser has explicit permissions defined in the permissions database; andidentify a second entity in the virtual machine system that is a childof the first entity using the labeling hierarchy of entities in thevirtual machine system.
 18. The non-transitory machine-readable storagemedium of claim 17, wherein to flatten the permissions database, theinstructions to cause the processing device further to: identify therole to which the user is assigned; identify a third entity in thevirtual machine system for which the role has permissions defined in thepermissions database; and identify a fourth entity in the virtualmachine system that is a child of the third entity using the labelinghierarchy of entities in the virtual machine system.
 19. Thenon-transitory machine-readable storage medium of claim 18, wherein toflatten the permissions database, the instructions to cause theprocessing device further to: create a separate entry in the flatteneddatabase view for each unique combination of the user and one of thefirst, second, third and fourth entities.
 20. The non-transitorymachine-readable storage medium of claim 16, wherein the indication ofwhether the user has permission to access the entity is affirmative ifthe entry in the flattened database view comprising the user and theentity is located.
 21. The non-transitory machine-readable storagemedium of claim 16, wherein the indication of whether the user haspermission to access the entity is negative if the entry in theflattened database view comprising the user and the entity is notlocated.
 22. The non-transitory machine-readable storage medium of claim16, wherein the entity in the virtual machine system comprises at leastone of a virtual machine, a virtual disk, a host server, or a virtualdata center.